It is known, for example from GB-A-1 350 661, to provide a thermal insulating panel comprising an outer porous envelope, for example of glass-fibre cloth, containing a block of consolidated dry particulate insulating material such as a microporous thermal insulation material. The insulation material is introduced into a porous envelope and pressure is applied to the exterior of the envelope to consolidate the insulation material into block form and to create a tension strain in the material of the envelope and thereby bonding the envelope to the surface of the block by penetration of particles of insulating material at the surface of the block into the pores of the envelope.
This known method of manufacturing panels of microporous thermal insulation material produces handleable panels having excellent thermal insulating properties. Such panels are widely used, for example in electric thermal storage heaters. The disadvantages of the panels, however, is that the edges of the panels are rounded. This rounded profile results from the manner in which the envelope is compressed in a platen press and makes it difficult to butt such a panel against a flat surface or, more particularly, against another similar panel of microporous thermal insulation material without the risk of poor thermal insulation performance in the region of the joint. There is thus a considerable demand for a microporous thermal insulating panel having relatively square, rather than rounded, edges.